A single SLM, such as a digital micromirror device (DMD) may have up to several million light modulators made from movable (or deformable) mirrors. Even with modern fabrication techniques and facilities, with such a large number of mechanical devices, it is likely that an SLM will have a few faulty light modulators. It is therefore imperative that SLMs be tested for proper function before they leave the factory so that improperly operating SLMs are not released for sale.
One commonly used prior art technique to test SLMs is to place an SLM into a test fixture, configure it to display a series of test images, and have a test operator evaluate the quality of the test images. The test operator can then determine if the SLM is operating properly based on the evaluation of the test images. The prior art technique can be extended by having the SLM display a test video clip and having the test operator determine the function of the SLM with respect to displaying motion pictures.
One disadvantage of the prior art that the qualitative evaluation of the image quality of the SLM by a test operator is a slow and potentially error-ridden process. The use of test operators to determine whether an SLM is functioning properly or not can lead to long test times, which can dramatically reduce the number of SLMs that can be tested. Additionally, the use of test operators can greatly increase testing costs. Furthermore, since the evaluation is a qualitative evaluation, the test results can be unreliable and difficult to repeat.
A second disadvantage of the prior art is that the test cannot measure dynamic characteristics of the SLMs, such as the synchrony of the operation of the mirrors, which mirrors are switching too fast or too slow, and so forth. Since the mirrors in the SLM switch on the order of micro-seconds, their operation is typically invisible to the test operators. While the dynamic characteristics are difficult to evaluate, they play an important role in the quality of the image produced by the SLMs.